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Fire History of a Mixed Conifer Forest in Guadalupe
1
Mountains National Park
Gary M. Ahlstrand
2
Abstract.--Fire scarred southwestern white pine
(P~
\. . 4.tJwbi6o.JUrl.i.6) cross sections from a 1700 ha study site in
the Guadalupe MOuntains were examined to determine the
historic role of fire in the forest. At least 71 fires have
occurred on the site since 1554. The mean interval between
major fires was 17.4 years for the period 1696-1922. No
samples were scarred after 1922. Reduced incidence of fire
during the past century coincides with changes in occupancy
and use patterns in the mountains.
STUDY AREA
INTRODUCTION
The study area consists of approximately 1700
ha in the upper portion of the South McKittrick
Canyon watershed in Guadalupe Mountains National
Park (fig. 1). The area sampled ranged in elevation
from 2150 to 2550 m and included the most heavily
visited portion of the park's high country.
The semiarid, continental climate of the area
is characterized by mild winters, warm summers and
summer showers. Lightning ignited fires occur
mainly during spring or early summer before the
onset of showers that accompany summer monsoons.
Associates in the mixed conifer forest include
Douglas-fir (P4eudo~uga menz-i.~-i.-i.), southwestern
white pine (P~ 4.tJwbi6o.JUrl.i.6), and ponderosa pine
(PbuL& pondeJL04a). Dry, south-facing slopes
support an open woodland of ponderosa pine, alli-
Tree stems with multiple fire scars are evidence that fire has been a significant ecological
factor operating in the past on a relict mixed
conifer forest in the high country of Guadalupe
Mountains National Park, Texas. The historic role
of fire in this ecosystem was little understood,
however. The abeence of fire in the recent past
has permitted thickets of conifers to become established in the understory throughout the high country.
It was not known if this represents a natural phase
in the life cycle of ~he forest, or if it resulted
from European man's activities in the area during
the past century.
Little information concerning fires in the
forest was readily available. Robinson (1969)
reported that fires occurred in the forest in
approximately 1858 and again in 1908 or 1909. A
native that has resided west of the park since 1906
recalled having seen flaming trees fall from high
cliffs in the mountains in about 1909 and smoke
from another fire in the high country in about 1922
(E. Hammock, personal communication). No fires of
any consequence have been reported for the forest
since 1922.
This study was conducted to determine the fire
history for a portion of the relict mixed conifer
forest. Cross sections from fire scarred tree stems
were studied in an attempt to identify specific fire
years, the incidence of fire in the study area, the
fire free interval for specific small areas within
the study area, and a general indication of past
fire intensities. Changes in the role of fire
resulting from shifting patterns of use in the
forest are also addressed.
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1Paper presented at the Fire History Workshop,.
Laboratory of Tree-Ring Research, University of
Arizona, Tucson, October 20-24, 1980.
2Ecologist, Carlsbad Caverns and Guadalupe
Mountains National Parks, Carlsbad, New Mexico
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Kilometers
Figure 1.--Map of the Guadalupe Mountains high
country study area showing locations of
sampled live cut (e) and dead (o) fire
scarred stems.
4
2
gator juniper (Junip~ deppeana) and pinyon pine
(P.l.rt.u.-6 e.c:iLLU.6). Where soil moisture is more available, as on slopes with some northerly aspect,
Douglas-fir and southwestern white pine dominate,
with ponderosa pine and pinyon pine included in
the association.
Indians are known to have occupied the area,
at least seasonally, until about 1870. By the
middle of the 19th century, parties of soldiers,
surveyors, settlers and gold seekers were passing
through the area on a trail just south of the
Guadalupe Mountains. European settlers were in
the area by the 1870's. By the turn of the century, cattle, horses, sheep and goats were being
run on rangeland surrounding the mountains, and
even in the high country (E. Hammock, personal
communication). Use of the high forested country
for summer range continued into the 1960's, but
was phased out between 1966 and 1970 after Congress
authorized the area to become a national park. The
area was officially dedicated and established as a
national park in September 1972.
with reasonable certainty within one year of another
scarred stem from the vicinity.
When feasible, two or more fire scarred ~ms
were sampled in a small area as in similar studies
(Houston 1973, Arno and Sneck 1977, Kilgore and
Taylor 1979). The occurrence of fire was determined
for two approximately one hectare sites. Seven
stems located within 100 m of each other were sampled on a west-facing slope near the crest of a
ridge, and three cross sections from stems that had
grown within 100 m of one another were taken from a
north-facing slope near the bottom of a small ravine.
A fire year was defined as any year in which at
least one sample was scarred by fire. Major fires
were defined as those in which 20 percent or more
of the samples alive at the time of the fire were
scarred, and at least two of the scarred samples
must have been separated by a minimum of 2 km.
All trees in fifteen 25 X 15 m plots were recorded by species and to the nearest diameter at
breast height (dbh) size class. Size class 1
included all stems less than 1 m tall; size class 2
included stems less than 5 em dbh; size class 3
consisted of stems 5-10 em dbh; and successive size
classes increased in 10 em dbh increments. Increment cores were taken from representative stems of
Douglas-fir and southwestern white pine so that
each size class could be correlated with tree age.
METHODS
Knowledge of the fire history for the relict
forest was considered important enough to justify
cutting cross sections from a number of fire scarred
stems. Transects were laid out in the study area
as described by Arno and Sneck (1977). Forty-eight
stems, all southwestern white pine, have been sampled to date (fig. 1). The cross sections came
from 3 living stems, 36 standing dead stems, 3
fallen dead stems, and 6 stumps left when a trail
was widened through a portion of the study area.
The location of each sample was noted on a 7.5
minute topographic map.
A master tree ring chronology was constructed
from indices calculated from measurements of annual
rings in two increment cores from each of 19 Douglasfir trees (Fritts 1974). The master chronology was
used to cross date the fire scarred sections. When
a sample section predated 1668, the earliest date
of the master chronology, a ponderosa pine chronology from Cloudcroft, New Mexico dating to 1515 was
used (Drew 1972).
Annual rings in the samples were measured under
30-90X magnification on a sliding stage micrometer
to the nearest 0.01 mm. Widths of annual rings were
plotted chronologically with fire scarred rings
noted. The sample plot was then cross dated with a
plot of the master chronoiogy.
Some fire scars were so distinct that it was
possible to identify the fire as having occurred
during the early, middle or late portion of the
growing season for a particular year from the
number and size of xylem cells formed prior to
injury of cambium. When scars appeared to have
formed between growing seasons, it was assumed that
the fire occurred during the dry, winter-spring
season unless a scar on a sample from a more sheltered site indicated that the fire burned late in
the previous year's growing season. Occasionally
a fire scarred ring was obscured by partial loss of
the ring in a subsequent fire, or decay. Such rings
were included only when they could be cross dated
RESULTS AND DISCUSSION
Data from 305 fire scarred annual rings contained in 48 southwestern white pine cross sections
indicate that fires of various sizes have occurred
in the study area in at least 71 of the years between
1554 and 1980 (fig. 2). Sixty-three of the fires
occurred before 1850 and none of the cross sections
were scarred by fire after 1922. The number of fires
per cross section ranged from 2-14 and the mean
70
60
10
1800
1900
2000
YEAR
Figure 2.--Incidence of fire in the study area as
determined from fire scarred sample stems.
Parameters for the regression line are: 15541842 segment, y = 0.251x - 399.8, r = 0.986;
1842-1922 segment, 7 = 0.0995x - 120.2, r =
0.993.
5
was open and park-like as recently as the early
1950's, large numbers of conifer seedlings were
becoming apparent about this time, nearly 30 years
after the last major fire.
A fire suppression policy has been in effect
for the area since coming under the stewardship of
the National Park Service. One ignition bumed
undetected in 1974 on an open, southwest-facing
slope in the study area. Less than two hectares
were burned before the fire died, and no trees
were found to have been scarred as a result of the
fire. Other fires originating outside the study
area might have spread into the area had they not
been contained by fire suppression crews while
still small.
MOst of the fires in the relict forest appear
to have been relatively low intensity ground fires.
Scarred stems in the forest are predominately those
of southwestern white pine. Fire scarred stems of
the more heavily barked Douglas-fir and ponderosa
pine were seldom encountered. Fire damaged stems
of young southwestem white pine usually die, and
older trees remain susceptible to scarring for many
years. Olily three of the· samples -were ·s·carred when
less than 15 years old. Nearly half the sample
stems were more than 50 years old when first scarred
by fire.
Pooled size class density data for southwestern white pine showed fewer trees present in
size class 3 than would normally be expected (fig.
4). Southwestern white pines of this size class
in the study area are ordinarily 50-100 years old.
A similar pattern was noted with Douglas-fir, except that both size classes 3 and 4 contained fewer
trees tban would be expected in a regular distribution (fig. 5). Comparison of age data from
interval between scars for individual cross sections varied from 11.5-68.3 years.
Because no stems were scarred by every fite,
the occurrence of fire is undoubtedly more frequent than indicated by the data. For example, 19
fires were represented by 35 scars that occurred
in seven cross sections taken from one of the
hectare sampling sites. Eleven of the fires were
represented by only a single scar in the sample.
Two fires each scarred four stems and the maximum
number of stems scarred by any fire was four. The
19 fires occurred between 1673 and 1922. During
this period the interval between fires ranged from
3-45 years and the mean fire free interval was 13.8
years. Fires scarred the three sample stems from
the other hectare site in 21 of the years between
1643-1879. The fire free period ranged from 2-37
years during this period and the mean interval
between fires was 11.8 years.
The mean interval for the incidence of all
fires detected in the study area for the period
1554-1842 was 4.7 years (fig. 2). Between 1842
and 1922 the fire free interval more than doubled.
None of the· sample stems ·were scarred· by fire
during the last 58 years.
Between 1696 and 1922, 14 major fires occurred
in the study area (fig. 3). The interval between
major fires ranged from 6-30 years, and the mean
interval was 17.4 years.
The reduced incidence of fire apparent after
1842 coincides with the ever increasing impact of
European man and the decreasing presence of Mescalero Apache Indians in the area. By 1880 most of
the Indians had been driven from the Guadalupe
Mountains. This suggests that many ignitions in
the forest prior to the mid-1800's were associated
with the use of fire by Indians. 'lbe high ·country
most likely received limited use between 1880 and
the early 1900's as European man settled in the
area.
Until this century, 30 years appear to have
been the maximuiD interval between major fires in
the study area. Thirty years elapsed between major
fires that occurred in 1879 and 1909. The last
major fire to occur in the study area was in 1922.
Increased use of the high country after 1930 as
summer range for livestock probably prevented cured
grasses from accumulating in quantities sufficient
to carry a fire any great distance. Longtime resi;..
dents recall that although the forest understory
STEMS/HA
400
Pinus strobiformls
200
6
25
~10
;:
c
_,
1
:::)
!
2
3
4
SIZE
5
u
5
6
~L·'~5
Figure 4.--Density of southwestern white pine by
size class in the mixed conifer forest,
Guadalupe Mountains National Park, Texas.
Size classes are: 1 o stems < 1 m tall; 2 ~
stems to 5 em dbh; 3= stems 5-10 em dbh;
and successive classes increase in 10 em dbh
increments.
2000
YEAR
Figure 3.--occurrence of major fires in the study
area, 1696-1922. Parameters for the regression
line are: y • 0.0566x - 94.55, r e 0.996.
6
Data from this study indicate that the mixed conifer forest was overdue for anotber·major fire by
the mid-1950's •. Many of the stems that now contribute to the dense understory thickets would have
been destroyed bad a fire occurred. A critical
situation exists in the forest·today. Ignition
under certain weather conditions with the present
dead and living fuel accumulation could result in
a devastating fire. Perpetuation of mixed conifer
forest is dependent upon finding an effective means
to reduce fuel loads while saVing most of the trees
in the canopy.
increment cores with diameter data for both species
indicate that growth rates for Douglas-fir·in
these size classes slightly exceed those for southwestern white pine in the study area. Many of the
trees expected in these size classes in a normal
distribution were apparently destroyed by the 1909
fire. During the 30 year interval since the last
major fire in 1879, fuels probably accumulated tc
levels that supported a more intense than usual
fire. Most of the trees in size classes 1 and 2
became established after the last major fire to
·occur on the study site in 1922. Dense ~bickets
of Douglas-fir have become apparent in the last
25-30 years (fig. 5).
LITERATURE CITED
STEMS/HA
Arno, Stephen F., and Kathy M, Sneck. 1977. A
method for determining fire history in coniferous forests of the mountain west. USDA
Forest Service General Technical Report
INT-42, 28 p. Intermountain Forest and Range
Experiment Station, Ogden, Utah.
6000
Pseudotsuga menzlesii
Drew, Linda G. 1972. Tree-ring chronologies of
western America. II. Arizona, New Mexico,
Texas. Chronology Series I, 46 p. Laboratory
(,of Tree-Ring Research, University of Arizona,
Tucson.
3000
Fritts, H. c. 1976. Tree rings and climate.
~67 p.
Academic Press, London.
Houston, Douglas B. 1973~ Wildfires in northern
Yellowstone National Park. Ecology 54:11111117.
1
2
3
4
5
6
7
8
9
Kilgore," Bruce M., and Dan Taylor. 1979. Fire
bist~ry of a sequoia-mixed conifer forest.
Ecology 60:129-142.
10
SIZE CLASS
Figure 5.--Density of Douglas-fir by size class in
the mixed conifer forest, Guadalupe Mountains
National Park, Texas. Size classes are the
same as for figure 4.
Robinson, James L. 1969. Forest survey of
Guadalupe Mountains, Texas. M. S. 'Thesis
71 p. • University of New Mexico, Albuquerque.
7